We will measure the blood flow to the MT-W9B mammary tumor and other organs in chronically catheterized W/Fu rats. Twenty-five micron radioactive microspheres will be injected before and after the left ventricular injection of the appropriate vasoactive drug. An integrated arterial blood sample will be withdrawn from the femoral artery before and after the injection of spheres so that we can measure blood flow to the various organs. We plan to construct time courses of the vasoactive responses to prostaglandin E and norepinephrine of the tumor and of other organs. The effect of alpha receptor and prostaglandin synthetase blockade on these time courses will be examined. The data will be reported as the resistance of the tissue after the injection of the drug (T) divided by the resistance of the tissue before the drug was injected (C). This T/C ratio for the tumor and other organs will be compared and appropriate statistical analysis will be performed. The validity of the microsphere technique for experiments of this nature will be ascertained by using simultaneous injections of 50, 25 and 15 micron spheres and comparing the blood flows obtained from each size sphere. Preliminary experiments have indicated that the 25 micron microspheres are an appropriate vehicle for these experiments and that the blood flows to the mammary tumor can be measured in the manner described.